a. Field of Invention
The invention relates to a power supply unit for an electronic device with capacitor buffering, a buffer capacitor being inserted between the supply voltage terminals and the lead terminals for voltage supply to the electronic device.
b. Description of the Prior Art
In power supply units for electronic devices care is often taken that in case of brief power failure the voltage supply for the electronic device will not immediately be interrupted. This is especially important e.g. in electronic timepieces or devices provided with volatile memories, because they lose their data content even after a brief failure of the supply voltage.
A common method for bridging brief power failures is to use a buffer capacitor, which is able for a short time to take over the current supply for the electronic device. In conventional devices the buffer capacitor is charged only to the operating voltage of the device. As the buffer capacitor discharges through the device, it soon reaches its minimum operating voltage, depending on the size of the buffer capacitor and current consumption of the electronic device. This then leads to failure of the electronic device. It is therefore necessary to use buffer capacitors of relatively high capacity to bridge a prolonged voltage failure. Such buffer capacitors are not only expensive, but they also require much space. Furthermore, many electronic devices function only in narrow voltage ranges, so that a decrease in operating voltage during the discharge of the buffer capacitor causes considerable disturbance.